1. Field of the Invention
The present invention relates to channelized sorbent material, and to methods of making and using the same.
2. Description of the Related Art
Sorbent materials of widely varying types are used in a correspondingly wide variety of industrial applications.
Examples include chemisorbent materials that are used to chemically react with impurity fluid species, for abatement of the impurity species in the fluid medium being treated, as well as physical sorbent materials that are employed to reversibly take up sorbable fluid species, e.g., for sorptive-based fluid and dispensing operations, as described in Tom et al. U.S. Pat. No. 5,518,528, and Tom et al. U.S. Pat. No. 5,704,965, the disclosures of which hereby are incorporated by reference in their respective entireties for all purposes.
The sorbent materials are frequently in the form of porous particles, having micro-pores of about 2 to 200 xc3x85 in diameter. The small-dimensioned porosity of the sorbent materials beneficially provides a correspondingly large surface area (typically measured in units of meters2/gram) per unit weight of the sorbent materials, with an associated large number of active sorption sites on and in the sorbent materials. At the same time, dimensions of the porosity in the sorbent materials have significant impacts upon diffusion rates of fluid species through such sorbent materials. Generally, diffusion rates of fluid species in a sorbent medium are determined by the mean free path length of the fluid molecules being sorptively taken up by such sorbent medium. The smaller the pores in such sorbent medium, the longer the mean free path length, and the slower the diffusion rates. Therefore, the small dimensions of porosity in conventional sorbent materials deleteriously constrain the ingress (in the case of irreversible chemical adsorption) and both the ingress and the egress (in the case of reversible physical adsorption) of fluid species into or from the sorbent materials through the small-sized, highly tortuous passages of the porosity.
Diffusion in relation to convective or bulk hydrodynamic flow is very slow in character due to the diffusion resistance caused by the small porosity of conventional sorbent materials. Particularly in reversible physical adsorption processes, such as in pressure swing and/or thermal swing adsorption processes wherein it is desired to separate a feed gas mixture to produce a purified or separated product, or in sorptive-based gas storage and dispensing applications in which it is desired to rapidly discharge the stored gas from the sorbent when the supply vessel flow control valve is opened, the diffusional resistance to extracting fluid from the sorbent medium imposes a significant constraint upon adsorption/desorption rates.
One method of countering the diffusional resistance of sorbent material in a fluid storage and dispensing vessel is described in U.S. Pat. No. 5,851,270 issued Dec. 22, 1998 to W. Karl Olander. In one approach described in this patent, an inert (non-sorptive) particulate material is interspersed with the active particulate sorbent particles, to combat resorption of previously desorbed fluid or interstitial fluid by the sorbent medium while such fluid flows out of the vessel to the dispensing assembly coupled to the vessel.
Another approach described in the same patent is the deployment of a porous diffusion tube for extraction of desorbed or interstitial gas. In such approach, the diffusion tube is arranged in the bed so that gas entering the tube flows directly out of the vessel containing the sorbent bed. This arrangement avoids further sorbent contact of desorbed gas entering the tube, which otherwise would result in repeated sorption/desorption/resorption/desorption during passage of fluid molecules through the bulk volume of the sorbent bed to the exit port of the vessel.
There is a continuing need in the art for improvements in the use and deployment of sorbent materials, particularly in respect of reducing diffusional resistance and increasing diffusion rates of fluid species in sorbent materials.
The present invention relates to channelized sorbent particles as well as to methods of making and using the same, wherein the sorbent particles have interior channels for facilitating ingress/egress of fluid into/from the porosity in the interior volume of such sorbent particles.
One aspect of the present invention relates to a channelized sorbent material having an average pore diameter and comprising sorbent particles having one or more interior channels, and wherein the interior channels have a transverse diameter at least one order of magnitude (10xc3x97) larger than the average pore diameter of the channelized sorbent material.
Another aspect of the present invention relates to a method for forming the channelized sorbent material as described above, comprising the steps of providing a sorbent precursor material, coating such sorbent precursor material around removable solid core bodies to form sorbent precursor particles, removing the removable solid core bodies to produce channelized sorbent precursor particles, and then converting the channelized sorbent precursor particles into channelized sorbent particles.
In a specific aspect, the present invention relates to a solid-phase porous sorbent material having an average pore diameter, wherein the solid-phase porous sorbent material comprises sorbent particles having one or more interior channels, and wherein the interior channels have an average transverse dimension at least one order of magnitude (10xc3x97) larger than the average pore diameter of the solid-phase porous sorbent material.
Such solid-phase porous sorbent material can be used in an adsorption-desorption apparatus for storage and dispensing of a sorbable fluid. Such an adsorption-desorption apparatus may for example include:
(a) a storage and dispensing vessel constructed and arranged for holding a solid-phase porous sorbent material, and for selectively flowing fluid in and out of the vessel;
(b) a channelized solid-phase porous sorbent material as described above, disposed in the storage and dispensing vessel at an interior gas pressure;
(c) a sorbable fluid adsorbed on the solid-phase porous sorbent material; and
(d) a dispensing assembly coupled in gas flow communication with the storage and dispensing vessel.
The dispensing assembly of such adsorption-desorption apparatus may be constructed and arranged:
(i) to provide, exteriorly of the storage and dispensing vessel, a pressure below the interior pressure, to effect desorption of sorbable fluid from the solid-phase porous sorbent material and flow of desorbed fluid through the dispensing assembly; and/or
(ii) to flow thermally desorbed fluid therethrough, wherein said dispensing assembly comprises means for heating the solid-phase porous sorbent material to effect thermal desorption of the fluid therefrom, so that the desorbed fluid flows from the vessel into the dispensing assembly,
The solid-phase porous sorbent material of the present invention may comprise any suitable material in any suitable shape. It may comprise, for example, silica, carbon molecular sieves, alumina, macroreticulate polymers, kieselguhr, carbon, and aluminosilicates. Preferred solid-phase sorbent materials include activated carbon materials.
Another aspect of the present invention relates to methods of making a channelized solid-phase porous sorbent material, including mechanically, chemically, or energetically forming one or more channels in a solid-phase porous sorbent material.
In one embodiment of the present invention, a channelized porous carbon sorbent material is manufactured by a method including the steps of:
(a) providing a pyrolyzable carbonaceous resin;
(b) coating the pyrolyzable carbonaceous resin on channel core bodies of a solid core material to form resin particles having coated cores, wherein said solid core material is insoluble in the pyrolyzable carbonaceous resin but is removable from the resin particles after their formation;
(c) removing the channel core bodies from the resin particles to form channelized resin particles having interior channels in the resin particles of the pyrolyzable carbonaceous resin; and
(d) pyrolyzing the channelized resin particles to produce corresponding channelized activated carbon particles.
Other aspects, features and embodiments of the invention will be more fully apparent from the ensuing disclosure and appended claims.